This invention is related to a process for making yarn, and in particular, to a process for making polytetrafluoroethylene yarn.
Fibers of polytetrafluoroethylene have been produced by slitting a polytetrafluoroethylene film into thin structures and then expanding and orienting these structures as shown in Gore U.S. Pat. No. 3,664,915, issued May 23, 1972. Also, continuous fibers of polytetrafluoroethylene have been prepared by blending viscous with a polytetrafluoroethylene dispersion and then extruding a filament and heating the filament to sinter the polytetrafluoroethylene and remove the viscous but this provides a dark brown fiber. To bleach the fiber, the fiber subsequently is passed through a nitric acid bath.
Neither of these processes form a polytetrafluoroethylene fiber which when made into a fabric will form high quality filters such as those used in electric power plants to remove ash from hot flue gas from boilers or those utilized by the chemical industry to filter hot corrosive liquids and gases.